Conventionally, this type of invention includes an optical module provided with a hollow housing, three optical fibers connected to wall surfaces of the housing, an optical filter (a half mirror, a WDM filter or the like) supported in the housing, and a cured product of a photocuring resin filling the housing, as described in Patent Literature 1.
In the method for manufacturing the optical module, the photocuring resin in the housing is cured by the light irradiated from the optical fiber to form three cores on both sides of the optical filter. Such manufacturing techniques are referred to as self-forming waveguide technique. Thereafter, a clad made of a material having a smaller refractive index than these cores is formed so as to cover the three cores.
Another conventional technique includes the formation of a filterless branch structure by self-forming waveguide technology, as described in Patent Literature 2, for example. In this conventional technique, it is mentioned that the angle of the two branched optical waveguide cores is limited to 10 degrees to 30 degrees inclusive, whereby the difficulty of optical axis alignment at the time of designing and manufacturing is eliminated and increase of optical loss can be suppressed.